1. Field of the Invention
The present invention relates to a head mechanism control apparatus which controls the load/unload operation of a head transducer from a recording medium, a disk drive unit using the head mechanism control apparatus, and an unload control method for a transducer head in a disk drive unit, and particularly to a head mechanism control apparatus which can reliably unload the transducer head.
2. Description of Related Art
In a disk drive unit, a head mechanism for supporting and moving a head slider having a transducer head may include a load/unload mechanism. The load/unload mechanism mounts a head arm having mounted thereon a head slider on a ramp provided in the vicinity of the inner periphery or the outer periphery of a disk. The load/unload mechanism unloads the head slider to a retract position outside the disk, and moves the head arm from the ramp to load the head slider over the disk. The head arm has mounted thereon a voice coil constituting a voice coil motor (VCM), for rotational movement of the head arm over the surface of the disk.
The load/unload mechanism climbs up the slope of the ramp while sliding in the unload direction to unload the head slider to the retract position, and it slides away from the ramp surface in the load direction to load the head slider over the disk. In addition, the load/unload mechanism does not intentionally bring the head slider into contact with the disk surface.
The head mechanism control apparatus for the load/unload mechanism controls the drive current (VCM current) that flows through the voice coil, thereby controlling the load/unload operation of the head slider. The loading of the head slider is performed when the main power supply of the disk drive unit is turned on, and when needed during the operation of the disk drive unit. The unloading of the head slider is carried out when the main power supply is turned off, and when needed during the operation of the disk drive unit.
Conventionally, the unloading of the head slider was performed by feeding a VCM current of a single polarity through the voice coil. The single polarity is the polarity for swinging the head arm in the unload direction, and it is the polarity opposite to the VCM current polarity for loading. Further, in the unloading when the main power is turned off (also called power off retract), the VCM current is generated from the counterelectromotive force of the spindle motor for rotating the disk. The spindle motor does not immediately stop the rotation if the main power is turned off, but it continues to rotate even after the main power supply is turned off mainly by the inertia of the disk for a while to generate the counterelectromotive force. The VCM current value in the power off retract depends on the magnitude of the above counterelectromotive force, and the magnitude of the counterelectromotive force depends mainly on the rotating speed of the spindle motor when the main power supply is turned off. Further, the time taken for the counterelectromotive force to become zero after the spindle motor stops the rotation depends mainly on the moment of inertia of the disk.
However, in the above conventional disk drive unit, there is a possibility that, if the unloading is initiated when the head arm is at a position on the disk outer diameter side which is near the ramp, the head arm cannot mount on the ramp overcoming the energy barrier by the slope of the ramp, and thus the unloading fails to be performed. This is because the distance for the head arm to approach the ramp after starting to swing in the unload direction on the disk is short, and thus it is not possible to ensure a sufficient kinetic energy for the head arm to overcome the above energy barrier. In particular, in the power off retract using the counterelectromotive force of the spindle motor, the above possibility is large because a large VCM current cannot be fed and the head arm cannot be accelerated with the short approaching distance. Further, in the power off retract, the lower the rotating speed of the spindle motor is when the main power supply is turned off, the higher the above possibility is.
The failure of unloading can lead to an accidental landing in which the head slider contacts with the disk surface. The disk surface is smoothed, and thus, if an accidental landing occurs, the head slider scratches the disk surface or sticks to the disk surface.
It therefore can be seen that there is a need in the art to provide a head mechanism control apparatus for a disk drive unit which can reliably unload the transducer head from a recording medium.